Porous ceramics-exhaust oxidation catalyst

ABSTRACT

Method of preparing temperature resistant exhaust oxidation catalysts suitable for use in land vehicle exhaust systems comprising a porous ceramic base impregnated with suitable oxidizing agents and the resulting catalysts. The porous ceramic base is prepared from a ceramic powder filled, plasticized polyolefin.

United States Patent Sergeys Dec. 16, 1975 POROUS CERAMICS-EXHAUST [56]References Cited OXIDATION CATALYST UNITED STATES PATENTS [75] lnventor:Francis J. Sergeys, Kensington, Md. 3,417,028 12/1968 Montgomery etal....... 252/ 55 R X 3,467,602 9/1969 Kocster 252/455 R [73] AsslgneeiGrace & (30-, New York 3,545,622 12/1970 Sakhnovsky et a1. 252/455 R x3,770,647 11/1973 Dautzenberg et a1 252/455 R X Filed: Kominami et a1 RX [21] Appl. No.: 380,032 Primary Examine rPaul F. Shaver Related us-Application Data Attorney, Agent, or FirmJ0seph P. Nlgon [63]Continuation of Ser. No. 82,918, Oct. 22, 1970, Pat. 57 ABSTRACT Methodof preparing temperature resistant exhaust ox- [52] Us Cl n 252/455252/463, 252/465, idation catalysts suitable for use in land vehicle ex-252/466 i i52/477 haust systems comprising a porous ceramic base im- 51Int. Cl. .Bdl 11/40 301 j 11/50 Pregnated with Suitable oxidizing agentsand the [58] Field of 5 R 463 466 PR sulting catalysts. The porousceramic base is prepared from a ceramic powder filled, plasticizedpolyolefin.

3 Claims, 9 Drawing Figures US. Patent Dec. 16,1975 sheetlofz 3,926,851

FIG. I

US. Patent Dec. 16, 1975 Sheet 2 of2 3,926,851

FIG-7 FIG. 6

FIG. 9

POROUS CERAMICS-EXHAUST OXIDATION CATALYST This application is acontinuation in part of application Ser. No. 82918 filed Oct. 22, 1970now US. Pat. No. 3,755,204.

This invention is a porous ceramic structure impregnated with suitableexhaust oxidation agents which is suitable for removing pollutants fromland vehicle exhaust fumes and the preparation of the catalyst. Thisinvention is also the method of producing the impregnated porous ceramicstructure.

The problem of air pollution is not a new one. However, the problem hasbecome aggravated in many cities in recent years. The air in most citiescontains substantial quantities of both oxides of nitrogen and theproducts of incomplete combustion of organic fuels. In the presence ofsunlight, photolysis of the oxides of nitrogen leads to the formation ofmeasurable quantities of ozone. The ozone, in turn, reacts with variousorganic pollutants to form compounds which can cause the manyundesirable manifestations of smog, such as eye irritation, visibilityreduction and plant damage.

When meteorological conditions prevent the rapid dispersion ofpollutants a smog condition results. Furthermore, it is now known thatin many cities a major portion of organic pollutants are derived fromunburned or partially burned gasoline in auto exhaust.

Another pollutant of much concern is carbon monoxide which isundesirable because of its toxic nature. This, too, is derived mainlyfrom exhaust emissions.

Almost since the advent of the automobile and diesel engine poweredvehicles, attempts have been made to solve the problem by renderingharmless and unobjectionable the noxious fumes which are the by-productsof internal combustion engines. Various devices and filters usingelementary catalytic materials, and since the I920s, variousmodifications of filters and mufflers, have been designed in an attemptto solve this problem. To date, none have met with success completeenough for practical applications. One of the most difficult problems toovercome is the fact that although a given purification system appearsto work initially within a short period of time it becomes thoroughlycontaminated and consequently useless. It does not seem feasible toinstall catalytic systems which must be periodically removed andrejuvenated because of the cost of such a system and such treatment.

Several investigators have realized that the only practical way to treatexhaust fumes to reduce hydrocarbon and carbon monoxide pollution is tooxidize the hydrocarbons to carbon dioxide and water and to oxidize thecarbon monoxide to carbon dioxide.

A wide selection of oxidiation catalysts has been produced in the pastvarying both in the chemical composition and physical structure. Withrespect to chemical composition, the ability of a wide variety of metalsand metal oxides, either alone or in combination, to catalyze thecomplete oxidation of hydrocarbons has been noted.

To be sufficiently efficient in the removal of hydrocarbons and, carbonmonoxide from internal combustion engine exhaust gases and to meet thestandards of maximum emission currently under consideration in thelegislatures of the various states, the catalyst for treating exhaustgas must become efficient within a very few minutes after enginestart-up and must maintain its activity throughout the various modes ofengine operation. A catalytic converter must maintain its cata lyticactivity for a period of not less than one year and preferably for over12,000 miles-of engine operation. The problem of excessively hightemperatures which are obtained when high concentrations of pollutantsare being oxidized must also be solved in this system. It is not unusualfor catalyst temperatures to reach 1600F. or higher. A normal catalyticsystem cannot withstand thermal degradation of the catalyst.

In this connection, the problem of conversion of carbon monoxide at thelow temperatures obtained in a catalytic muffler system at the start-upperiod of the engine operation is particularly troublesome. A catalystmust be active initially to be acceptable for use in an auto exhaustcatalytic system. It is not sufficient that a catalyst will have a goodactivity after the engine is warmed up and the catalyst bed is at atemperature high enough to cause exhaust vapors passing through the bedto be oxidized to carbon dioxide and water.

The catalytic systems which have been devised to give satisfactoryresults for carbon monoxide conversion frequently suffer from relativelypoor conversion of hydrocarbons. Since the ideal catalytic system givesa good conversion of both of these exhaust gas components, this problemis of prime importance.

An additional difficulty in the preparation of auto exhaust catalystsand the design of suitable mufflers for the integration of the exhaustcatalyst into the conversion system is the problem caused by thepresence of oxides of lead and particles of metallic lead in theexhaust. This lead results from the conversion of tetraethyl lead whichis still the most commonly used gasoline anti-knock additive. In thepreparation of gasolines, a quantity of tetraethyl lead is added to thegasoline at the refinery to impart anti-knock properties to the fuel. Inaddition to the tetraethyl lead, various compounds such as ethylenebromide, for example, are added, which convert the lead to volatilecompounds which have an appreciable vapor pressure and are thus carriedout of the engine into the exhaust system. The presence of thesecompounds causes problems with catalytic systems in that these leadsalts, in addition to physically coating the individual catalystparticles, cause decreased attrition resistance by deterioration andbreakdown of these particles.

Another difficulty in the removal of pollutants from auto exhaust fumesis the expensive method of producing porous ceramic bodies of sufficientnumber to meet todays needs and which are able to withstand thetemperatures to which they are necessarily subjected in the exhaustsystems of land vehicles.

The use of organic binders for ceramic powders is a well establishedcommercial practice. Attempts to use fillers in a similar manner toextend or reinforce the more crystalline polyolefins, however, have metwith failure. Brittle products are generally obtained even with moderatefiller concentrations. Previous attempts have been made to producepolyethylene/filler blends using conventional inert fillers alone.Occasionally, these blends are found to have greater tensile strengththan the unfilled polymer but when the polyethylene is heated it tendsto have a low viscosity and is therefore not easily workable.

On the whole, reported studies of polyolefin (especiallypolyethylene)/filler blends indicate that satisfactory products arerarely obtained. Small amounts of some inorganic materials can beblended into polyethylene as pigments, but serve no other purpose.

More recently, however, it has been found that it is l possible toprovide a low cost, tough, flexible polyolefin/filler composition. Aprocess for preparing such a composition is described in Australian Pat.No. 277,981 and British Pat. No. 1,044,502. The latter patent disclosesa method of producing a composition containing (i) a polyolefin ofmolecular weight sufficiently high to give it a standard load melt indexof substantially zero (ii) an inert filler, e.g. ceramic powder, and(iii) a plasticizer. The composition described therein comprises l80% byvolume polyolefin, 60% by volume filler material, and l585% by volumeplasticizer.

The former patent, Australia Pat. No. 277,981 discloses a similar methodof producing a composition which comprises 595% by volume polyolefin,550% by volume filler, and 540% by volume plasticizer.

Attempts to form ceramic structures have also met with little successbecause in the early stages of firing the structures became distorted oreven cracked. Attempts to overcome this difiiculty have beenunsuccessful. Various mixtures of thermoplastic binders have been foundto be entirely unsuccessful.

Porous ceramic structures are used for catalyst supports, absorptiondrying, separation of liquid phases, etc. Generally, porous ceramics areeither prepared by one of two methods. The first method consists offiring an alumina silicate with a small amount of flux to form a slightglassy bond. In the other method alumina grain is fired with a ceramicmaterial which melts and holds the grain together. Although both ofthese methods produce excellent porous ceramics, both are timeconsumingand production is slow. v

Porous ceramic structures which are used in filtration processes allowcleaning without halting flow of the material being cleaned. Cleaning isoften accomplished, in the case of organic materials, by ignition tol200-l600F. without damage, and also by mechanical brushing. In chemicalprocessing gas is forced through a catalytic porous structure enablingthe purified gas to pass through the structure and the porous ceramicstructure to retain the contaminants. However, in all cases there existsthe slowness of production of the porous structure.

Attempts to prepare porous ceramic articles have met with failure inthat there has been an absence of success in preparing a sturdy porousceramic article from a ceramic powder filed, plasticized thermoplastic.

It is accordingly an object of this invention to provide a method forproducing porous ceramic bodies containing land vehicle exhaustoxidizing agents capable of removing pollutants from a vehicles exhaustfumes.

It is further an object of this invention to produce a porous catalystcontaining ceramic structure from a flexible low-cost polyolefinmaterial. It is a further object of this invention to produce a porousceramic catalyst from a highly filled polyolefin material containing aplasticizer. It is a further object of this invention to produce aporous ceramic article suitable for use as a catalyst support by thesteps of (i) preparing a composition comprising a ceramic filler, aplasticizer, and a polyolefin material, (ii) shaping the material, (iii)extracting the plasticizer, (iv) burning the shaped material to removethe polyolefin, (v) firing the ceramic material which remains, and (vi)impregnating the ceramic material with an oxidation catalyst.

It is a further object to produce a porous ceramlc exhaust catalyst.More specifically, it is an object to provide a low-cost, easy to make,porous ceramic automobile exhaust catalyst. Further objects will beapparent from the following description of this invention.

FIG. 1 shows the ceramic powder'filled, plasticized polyolefin which hasbeen rolled up prior to removal of the plasticizer and polyolefin.

FIG. 2 shows the finished product of this invention which is obtainedafter the process of this invention has been completed (only thesintered ceramic material remains).

FIG. 3 shows the ceramic powder filled, plasticized polyolefin after ithas been fabricated into a plastic sheet containing ribs.

FIG. 4 shows the final product obtained when the polyolefin materialshown in FIG. 3 is rolled up and the process of this invention isfollowed. I

FIG. 5 shows a sheet of ceramic powder filled, plasticized polyolefinmaterial having ribs on both sides.

FIG. 6 shows the resulting product when FIG. 5 is rolled and the processof this invention is followed.

FIG. 7 shows the product obtained when a foamed polyolefin material isused.

FIG. 8 shows how a ceramic powder filled, plasticized polyolefinmaterial is arranged to produce the final product shown in FIG. 9.

After the product of FIG. 9 is impregnated with the oxidizing catalystit still has the same of the final fired product, e.g., that of FIG. 9.

SUMMARY OF THE INVENTION This invention is a novel method of producingporous ceramic catalyst-containing structures suitable for auto exhaustsystems. The method comprises shaping a filled polyolefin materialcontaining a plasticizer, extracting the plasticizer, burning-off thepolyolefin, firing the porous shaped ceramic structure, and impregnatingthe structure with an engine exhaust oxidizing agent. This inventionfacilitates production of porous ceramic structures containing suitablepassages thereby increasing the effectiveness of contacting a gas orliquid with a catalyst supported on the structure. Various shapedceramic exhaust catalyst structures can easily be prepared by theutilization of this method.

More specifically, I have found that a porous ceramic structure producedby the herein disclosed method can be impregnated with exhaust catalystsused to remove pollutants from land vehicle exhaust fumes.

DETAILED DESCRIPTION OF'THE INVENTION As mentioned previously, it hasbeen found that a porous ceramic structure can be prepared from astarting material comprising a ceramic powder, a polyolefin, and aplasticizer.

Since the instant invention requires a porous structure invention as astarting base for subsequent catalytic impregnation, the structure (andits method of preparation) will here be described in detail; se'eespecially Examples 1-22.

It is to be understood that the references made to polyolefin aregenerally to high molecular weight polyethylene.

More specifically a polyolefin of very high molecular weight (eg. atleast 150,000) is a good binder for ceramic powder and can tolerate highfiller loadings without becoming brittle when a plasticizer is present.This is quite unlike-conventional thermoplastics, e.g. polyethylenehaving a molecular weight of around 60,000 to 100,000 which yieldsbrittle products at relatively low filler concentrations. Plasticizersmust be incorporated into these highly filled blends to provide goodflow characteristics and to facilitate mixing without causing excessiveloss of flexibility. Tough, flexible compositions therefore, can beproduced from a three component system consisting of (1) a highmolecular weight polyolefin; (2) a filler; and (3) a plasticizer.

Each of the above stated components is essential for attainment ofdesirable performance of the binder system. The components of thecomposition can vary in the following amounts and still provide aworkable plastic composition: polyolefin 5-67% by volume, plasticizer-80% by volume, and filler 15-80% volume of polyolefin 10-70% by weight,plasticizer 10-70% by weight and filler -90% by weight. However, preferable ranges are polyolefin 5-50% by volume, plasticizer 20-60% by volume,and filler 20-50% by volume. The high molecular weight polymer confersstrength and flexibility to the initial composition. The plasticizer, ofcourse, also provides flexibility, but its primary role is to increasethe melt index and thus produce a processable compound and to provideporosity for the combustion step and to facilitate the initialdispersion of filler into the matrix.

A wide variety of inexpensive, finely divided ceramic materials isavailable for use as fillers. The following types are included asexamples but are not limiting in this category: (a) metal oxides andhydroxides, especially those of silicon and aluminum such as 60 alumina,(b) metal silicate and aluminates; naturally occurring clays, mica,etc.; precipitated silicates, synthetic zeolites, etc., (0) titantes,zirconates, and compositions useful for making capacitors andpiezoelectric devices, and (d) ferrite and garnet compositions useful inferromagnetic devices.

More specifically, the fillers which are preferred include mullite (3-AlO,-, ZSiO synthetic mullite compositions, zircon mullite, magnesiumaluminate, spinel, and cordierite (2MgO.2Al O .5SiO

It has been found that fillers of very high surface area require moreplasticizer to be processable in the plastic than fillers of lesssurface area and are very effective in retaining the oil, but generallygive products with unmeasurably low melt indices. Additionally, ceramicpowders of high surface area cannot be compounded to as high a fillerloading capacity as those of a low surface area. Such fillers can beused in combination with fillers of low surface area to help retain theplasticizer.

As used herein, the terminology plasticizer is intended to define amaterial which performs five functions. First, the addition of theplasticizer will improve the processibility of the composition, i.e.,lower the melt viscosity, or reduce the amount of power input which isrequired to compound and to fabricate the composition. As explained morefully hereinafter, the melt index is an indication of the processibilityof the composition, the melt index increasing as the molecular weightand viscosity decrease. Similarly, a torque decrease indicates a lowermelt viscosity and improved compounding ease (faster mixing cycle, andlower power requirements). The second function of the plasticizer is toimprove the flexibility of the interim plastic composition. The improvedflexibility is reflected in such measurements as the elongation atfailure, the elongation at yield point, Spencer impact, and tensionimpact. The third function of the plasticizer is its utility in theproduction of the final porosity. Fourth, when the plasticizer iseventually removed the viscosity of the material is then increased.Fifth, removal of plasticizer facilitates removing gaseous combustionproducts which are produced when the polyolefin is burned-off. Theplasticizer is the component of the polyolefin/filler/plasticizercomposition that is easiest to extract. The extraction can be performedwith water or with any number of commercially available organicsolvents, with the particular-solvent depending upon the particularplasticizer used. It is especially advantageous, however, to use aplasticizer which is soluble in water. By using a water solubleplasticizer, the extraction process will be more economical due to thelow cost and relative safety of water in comparison to that of organicsolvents. The extraction process will also be much safer as there willbe no fire or toxicity hazards encountered.

Examples of the numerous suitable plasticizers are the following:

a. sulfonamide, coumarone-indene, asphalt, etc.

b. hydrocarbons white mineral oil to Bunker C fuel oil Examples of thenumerous suitable water soluble plasticizers are:

a. glycerin, glycerol monoacetate, etc.

b. diethylene glycol c. propylene glycol, dipropylene glycol d.trimethylene glycol, tetramethylene glycol, 2, 3-

butylene glycol, etc.

e. triethyl phosphate f. water soluble polymeric materials, such aspolyacrylic acid, and polyvinyl pyrrolidone.

It is also possible to use various combinations of the above mentionedplasticizers, such as a water soluble and a water insoluble plasticizerwith a suitable filler and high density polyethylene.

Most of the work was carried out using commercial particle form highmolecular weight polyethylene, having a standard load (2160g.) meltindex of 0.0, a high load (21,600 g.) melt index of 1.8, a density of0.95, and a viscosity of 40 measured as 0.02 grams of polymer in g.decalin at C. This polymer can be prepared by the method given in US.Pat. No. 2,825,721 using an ammonium fluoride treated chromium oxidecatalyst. When the term particle form is used herein, it refers to theaforesaid polymer. However, any commercially available polyethylenehaving a standard load melt index of substantially O is entirelysatisfactory. Many of the illustrations to be described usedpolyethylene having a standard load melt index of 0.00, a high load meltindex of 0.01, and a viscosity of 9.3 measured as 0.02 grams of polymerin 100 g. decalin.

It is noteworthy that melt index is a measure of polyethylene flow atstandard conditions of temperature, pressure, and time through anorifice of defined diameter and length as specified in ASTMD 1238-GSTcondition F (Measuring Flow Rates of Thermoplastics by ExtrusionPlastometer). The rate of extrusion in g/ 10 minutes is the melt index;and it is used to indicate the average molecular weight of a polymer.The lower the molecular weight of a polymer, the more rapidly itextrudes, and therefore, melt index increases as molecular weightdecreases. By high-load melt index (I-ILMI) is meant melt indexdetermined by the procedure of ASTM-D-1238-65. Condition E, except thata weight of 21,600 g. is used.

However, it has been found that in addition to high molecular weightparticle-form high density (0.93 O.97) polyethylene, high molecularweight low density polyethylene, high molecular weight polypropylene,and high molecular weight particle form ethylene-butylene copolymer canalso be used to give entirely satisfactory results.

Further, depending upon the desired physical properties of the finalproduct, the high molecular weight polyethylene can be blended withstandard commercial lower molecular weight polyethylene, bearing in mindthe fact that if the overall molecular weight of the blended polymerbecomes too low, the interim plastic product is apt to become brittle.

The technique which was employed to produce the composition can bedescribed as follows. In most cases the various components were premixedat room temperature in a dough-mixer. However, in some cases the fillerand plasticizer were slurried together at room temperature in a volatilesolvent which was evaporated before the materials were combined with thepolyethylene. The polyethylene/filler/plasticizer dry blends (in somecases a dough, in others a powder) were then mixed in a BrabenderPlastograph.

The following mixing procedure was also found to be satisfactory. Thepolyolefin was added to the mixing chamber which was preheated to 180C.When the polyolefin fluxed, the filler was added, followed by theplasticizer. In those areas where the initial portions of the fillerproduced extremely high torque, portions of the plasticizer were addedto bring the torque down before the rest of the filler was added.Generally five minutes was allowed to melt the polymer and add thefiller. It was found that when the filler is added as a dry powder itfrequently accumulates in dead spots on the blades or in the mixingchamber. For this reason, a method of double compounding is used. Thisis accomplished by recovering all the material from the plastograph, andthen replacing it in the plastograph to get the material from the deadspots adequately dispersed.

It is possible to produce the composition by mixing the components inany order. Generally the components are mixed in the plastograph at 30to 200 RPM until the mix appears to be uniform.

The final product blends can vary in overall composition according tothe desired porosity in the final product. It has been determined thatthe greater the overall surface area of the filler, the more plasticizerthat can be incorporated. Further, the relative proportions of theingredients can vary greatly, depending both upon the desired physicalproperties of the intermediate product and the final product.

The polyolefin/filler/plasticizer blends were normally pressed instandard fashion common to the art on a hydraulic press into 0.020 inch(nominal thickness) sheets at 125 l 75C. for about three minutes atabout 500 psi. The only property of interest in the intermediate plasticproperty is sufficient flexibility and strength to be subjected to theforming, fusing (where indicated), and extraction steps necessary beforeburning and firing.

The method of shaping, pressing (or fabricating), is directly related tothe type of porous ceramic structure which is desired.

In one embodiment a smooth filled thermoplastic sheet is rolled up as inFIG. 1 and then subjected to the process of the invention. The resultingceramic body (FIG. 2) is then high in microporosity and is readilyimpregnated with oxidation catalysts.

In another particular embodiment the filled polyolefin sheet is preparedwith integral ribs as shown in FIG. 3. Following the preparation of thefilled polyolefin it can be prepared as shown in FIG. 3 by any ofseveral methods of fabricating such as molding, extrusion, embossing orcalenderig. The sheet can then be rolled up as in FIG. 4. The ribs 1 canbe toward the inside or the outside of the roll. The ribs whose shapecan be continuous, discontinuous, cylindrical (like tufting in a carpet)etc. act as spacers to provide macroporosity. This type of shaping willproduce a honeycombed ceramic structure exhibiting both micro andmacroporosity. The microporosity is achieved as the polyolefin iseventually burned out.

A slightly different honeycomb structure can be obtained by rolling thesheet at any angle of less than (FIG. 6) when a polyolefin materialhaving integral ribs (2,2) on both. sides FIG. 5, wherein the ribs oneach side of the sheet are not parallel in order to avoid nesting of theribson contacting sides) is used. Such a micro-macro porous ceramic bodyassures a turbulent flow of gas and is particularly well-suited to serveas a catalyst support having a high capacity for contacting a gas suchas exhaust fumes from an automobile, in accordance with the instantinvention.

The fusion or heat sealing is carried out by heating the filledpolyolefin sheet to a temperature of from about C to just below the burnoff point preferrably 500C.

It is possible to provide additional pore volume in a porous ceramicstructure by foaming the filled polyolefin composition. (The foaming canbe accomplished by the addition of any known foaming agent to thefilled; plasticized polyolefin composition.) Such a composition can thenbe fabricated into any foamed shape by normal plastic processing meansand later developed into a porous ceramic structure (FIG. 7).

In yet another embodiment nets of filled polyolefin (FIG. 8) (ashereinafter described) can be fused together (FIG. 9) to form athree-dimensional network which, when converted into a microporousceramic is useful as a support for a catalyst in gas contactingcatalytic processes. This structure is readily impregnated withcatalysts in accordance with this'invention. This method produces a lowdensity ceramic structure with a large surface and having no straightpaths through the structure, thereby providing a tortuous path and ahighly turbulent flow of gas. The interim fused structure can beprepared by layering net or rolling up of net, both prior to fusing theadjacent layers.

Following fusion the plasticizer is then extracted. This can beaccomplished by any solvent in which the plasticizer is soluble. Forexample, when using a plasticizer such as mineral oil, hexane is asuitable solvent. When a water soluble plasticizer such as diethyleneglycol is used, water is a suitable solvent. The removal of theplasticizer results in the formation of a microporous structure. Inaddition to providing greater surface area, the extraction of theplasticizer prior to burning off the polyolefin is of great value sincethe formation of the micropores aids in removing gaseous combinationproducts which are formed when the polyolefin is burned off.

After the plasticizer has been extracted the structure is heated toabove the degradation temperature of the thermoplastic so as tocompletely burn off the polyolefin. The degradation temperature will, ofcourse, vary with the choice of polyolefin. For the high viscositylinear polyethylene that I prefer to use, a temperature in the range ofat least 240 to 260C. is greatly preferred to initiate degradation.

At a temperature of about 240C. (when polyethylene is the polyolefin)the structure begins to turn black and at about 700C. the structurebegins to turn white, indicating that the thermoplastic has entirelyburned off.

When the thermoplastic is completely burnt off, the temperature isincreased to that it which the particular powder sinters into amonolithic structure, still retaining the micro-porosity. When using thepreferred ce ramic powder, oz-alumina, a temperature of aboutl300-l450C. is recommended. The temperature is held at the sinteringpoint for about 2 hours and then the structure is allowed to cool slowlyto room temperature. The cooling time is generally about 34 hours.

The resulting porous ceramic body appears identical in shape to theoriginal plastic structure except that a slight linear shrinkage, -20%,takes place.

In addition to the basic procedure heretofore described, i.e. mold,roll, heat the structure to just below the burn off point to fusethermoplastically, extract the plasticizer, burn off the polyolefin, andfire the ceramic structure, variations of this procedure also result inexcellent porous ceramics.

The method of impregnation is not critical, but rather any method whichis capable of placing the catalytic components within the porousstructure is sufficient. Although impregnation is the most practicalmethod of depositing the catalytically active agents on the monolithsother processes, such as coating for example, also give satisfactoryresults.

In the deposition of a noble metal on the monolith, for example, it maybe practical to prepare a slurry containing a solution of a salt of thenoble metal and add an agent to convert the noble metal to an insolublespecies prior to depositing the slurry on the monolith. Direct coatingof the monolith with an insoluble cata' lytically active agent is alsocontemplated in the process of this application.

The particular catalytic components used are not specific to thisinvention. Any of the various catalytic components suitable for removingair polluting fumes from auto gases are operable.

Some of the useful catalytic compositions are disclosed in US. Pat. Nos.3,288,558; 3,295,918; 3,304,150; 3,322,491; 3,338,666; 3,346,328; 3,455,843 and 3,470,105. These catalytic compositions include the followingcatalytic components in percentages by weight of the total catalyststructure.

Catalyst 1 Catalytic 10% CuO. 4.0% CEO 0.027: Pd. Components Catalyst 2Catalytic 8% CuO. 12.07: MnO 0.02% Pd. Components Catalyst 3 Catalytic4% CuO. 6% MnO:. 4% CEO Components 0.02% Pd.

Of course, other catalytic compositions are also useful.

A particularly suitable method of impregnating these catalyticcomponents onto the porous material is that described in US. Pat. No.3,455,843 wherein the copper-palladium is impregnated into the porousstructure by means of a copper-palladium solution followed byimpregnation with the chromia (Cr O- by vacuum impregnation (Catalyst1). The components of Catalyst 2 are therein impregnated into the porousstructure by immersing the structure in a copper-manganese-palladiumsalt solution. When this is followed by impregnation with the chromia byvacuum impregnation, a porous ceramic structure containing the catalyticcomponents of Catalyst 3 was thereby prepared.

The following examples will aid in further explaining the invention.

EXAMPLE 1 An alumina filled polyethylene composition designatedComposition A and containing the following components, 8.6 gramsparticle form linear polyethylene of 0 Melt Index (SLMI), 76.8 grams a-alumina, and 28.8 grams of a mineral oil with approximately saturates(visocosity: ss/w at F 547, refractive index 1.4932 i 0.0003, andspecial gravity at 15C. 0.9036 0.9071) available commercially asShellflex 411 was prepared by compounding the raw materials in aBrabender Plastograph at 170C. This composition was then labeled PlasticA and was then pressed to a 12 mil sheet in a hydraulic press with 20tons force. then repressed in a mold to give a ribbed sheet with a 6 milbackweb, and about 25 mil wide with a taper, 30 mil high ribs spacedinch apart. From the ribbed sheet, strips were cut 30 mm. wide by 8inch, and these were rolled up tightly with the ribs in the direction ofthe axis of the roll, forming a honeycomblike cylinder. This wasinserted into a tight fitting, glass tube, and heated to heat-seal theconsecutive layers of the spiral roll of ribbed sheet at about C.

The cylinder was then cooled and immersed in hexane for 30 minutes toextract substantially all the mineral oil, then dried and heated in afurnace in an oxidizing atmosphere first to about 250C. (over a periodof about 2 hours) when degradation began as evidenced by the black colorof the structure. The temperature was slowly increased and about 2 hourslater and at about 700C. the structure turned white, indicating that theburn off of the polyethylene was complete. The temperature was thenslowly increased and about 2 hours later the temperature reached l450where it was held for about 2 hours to sinter the remaining ceramicpowder and cooled slowly (about 4 hours).

The honeycombed porous ceramic body (designated Ceramic body A) whichresulted appeared identical in shape to the original plastic structure,but the dimensions were slightly smaller. The body had good physicalstrength and was hard enough to scratch ordinary glass.

Weight percent can readily be converted to volume percent by dividing agiven component by its density and recalculating on a percentage basis.Thus, in Example l, the components in weight percent can be converted tovolume percent as follows:

1 ll l2 Volume in Propor- Volume Component WLV: Density tional Parts 7rPolyethylene 8.6 I 8.6 8.6 56.6 15.2 or-alumina 76.8 4 19.2 19.2 56.633.) Mineral oil 28.8 +1 28.8 28.8 56.6 50.9

An approximation EXAMPLE 4- Volume percent is converted to weightpercent by the same procedure, except that the volume percents aremultiplied by the densities of the respective components.

in the generalized description, and in the claims, it will be noted thatthe invention is defined in volume percent. This mode of definition isfrequently preferred, since the volumes of the respective components aremore generally important than their respective weights as regardscontrol of processability of the polymer/filler/plasticizer mixture andability of the product to sinter to a strong ceramic product and yetretain useful porosity.

EXAMPLE 2 Another sample of Composition A" was used to prepare anothersample of Plastic A which was then pressed to a mil sheet in a hydraulicpress with 20 tons force, then repressed in a mold to give a-ribbedsheet with 6 mil backweb and ribs on opposite sides of the sheet,crossing at 90 each mils wide (tapered) and mils high. and space /8 inchapart. From the ribbed sheet strips were cut at 45 angles to both ribs30 mil wide by 8 inch, and these strips were rolled up. Fusing was thenaccomplished by passing hot air through the strip as in Example 1. Thefused strucuire was then cooled and immersed in hexane for 30 minutes toextract the plasticizer, dried and heated in a furnace first to about250C, then to about 700C. and finally to 1450C., as in Example 1. Thehoneycombed porous ceramic body (designated Ceramic Body B) whichresulted appeared identical to the original plastic structure, but thedimensions were slightly smaller. This body also had good physicalstrength and was hard enough to scratch-ordinary glass.

EXAMPLE 3 Another sample of Composition A was used to prepare anothersample of Plastic A which was then made into a foamable material(designated Plastic Foam A) by the addition of 0.25% of a chemicalblowing agent, azo-bisformamidev The foamable material was heated at200C. at which temperature the foaming agent decomposes. The foamedmaterial was then watar-cooled and fused as in Example 1. Theplasticizer, mineral oil, was then extracted by dipping the shapedmaterial into hexane for 30 minutes. Afier drying at room temperaturefor 30 minutes, the shaped material was heated in a furnace to about250C, then 700C. and finally to 1450C. as in Example 1 to burn off thepolyethylene and to sinter the ceramic powder and cooled slowly. Theporous ceramic body (designated Ceramic Body C which resulted appearedidentical in shape to the original foamed structure except that thedimensions were slightly smaller. This ceramic body provided additionalpore volume and was less dense than Ceramic Bodies A and B.

Another sample of Composition A was used to pre pare a sample of PlasticA which was pressed to a 20 mil sheet in a hydraulic press with 20 tonsforce and then pressed between two crossed, groved press platens toproduce a sample of plastic net. The net was cut, rolled up, and thenfused together by heating at a. temperature of about 150C. to form athreedimensional net structure which was then cooled to roomtemperature. Extraction of the plasticizerand heating to burn off thepolyethylene and sinter the ceramic structure took place as in Example1.

The porous ceramic body (designated Ceramic Body D) was of low density(48 lbs/hf), had a large surface, and without straight paths. The bodyalso had good physical strength and was hard enough to scratch ordinaryglass.

EXAMPLES 5 and 6 Example 1 was repeated except that a high molecularweight ethylene-butene copolymer commercially available from AlliedChemical Company (0 standard load melt index, 1.8 high load melt index,0.943 density, a reduced solution viscosity of 4.0 and a molecularweight of about 180,000) was used in place of polyethylene in Example 5.in Example 6, ll-lifax 1901. a high density linear polyethylene (0standard load melt index, and a molecular weight of about 2 million) wasused in place of the polyethylene. In each case, ceramic bodies wereobtained exhibiting good strength.

. Various other fillers as explained herein were used in place of thea-alumina of Example 1. Some of the particularly good ceramic powdersadaptable to this invention were the following:

EXAMPLES 79 in Example 7 a mullite composition of by weight raw kyanite(-325 mesh, Al O .SiO and 25% by weight South Carolina kaolin(commercially available from l-luber Corp.) was used in place of the ct-alumina. in Examples 8 a mullite composition of 75% by weight calcinedmullite (325 mesh, a 70% alumina bauxiteelay calcine) and 25% by weightSouth Carolina kaolin (Huber Corp.) was used in place of the or-alumina;and in Example 9 a mullite composition of calcined mullite (325 mesh, 2170% alumina bauxite-clay calcine) and 15% Jackson ball clay(commercially available from Kentucky-Tenn. Clay Corp.) was used inplace of the a-alumina. In each case the sintering tem perature wasabout l225-l350C. With each ceramic powder a ceramic body of goodstrength was obtained.

EXAMPLE 10 in this example a zircon-mullite composition of 50% calcinedmullite (325 mesh, a 70% alumina bauxiteclay calcined). 25% groundzircon (325 mesh) and 25% South Carolina clay was used in place of thea- 13 alumina of Example 1. The rest of theproced ure was the same asExample 1 except that the sintering tem' perature was l225l350C. Aceramic body of good strength was obtained. I

EXAMPLE ll Example 1 was repeated except that in place of aalumina. aspinel (commercially available from W. R. Grace & Co.) prepared from thedecomposition of high purity magnesium aluminate was used. The sinteringtemperature was l225-l 350C. and a porous ceramic body of good strengthwas obtained. I

Another preferred ceramic powder is that commonly referred to ascordierite. which is a zeolite of the formula 2MgO.2Al O .5SiO Thefollowing cordierite compositions were prepared and used as the ceramicpowder in the plastic composition.

EXAMPLES 1245 In Example 12 a cordierite composition was prepared byadmixing 50% by weight Florida kaolin and 50% by weight sierralite arelatively pure prochlorite commercially available from United SierraDiv., Cyprus Mines Corp). The mixture was substituted for the a-aluminaof Example I. The remaining procedure of Example 1 was followed. Theresulting good strength, porous ceramic body was sintered at l200-l225C.In Example 13 the procedure of Example 1 was followed except that acordierite composition was prepared from 75% by weight Florida kaolinand 25% by weight tale. The porous ceramic body which was obtained aftersintering at l300C. was of good strength. In Example l4 a cordieritecomposition of 72.5% by weight Florida kaolin, 22% by weight talc, and5.5% by weight magnesium carbonate was substituted for the a-alumina ofExample 1. The rest of the procedure of Example I was followed exceptthat sintering took place at l275l300C. and a strong porous ceramic bodywas obtained. In Example 15 the a-alumina of Example 1 was replaced witha cordierite composition prefaced by admixing 68% by weight Floridakaolin, 15% by weight talc. and 17% by weight magnesium carbonate. Therest of the procedure of Example I was followed and a strong porousceramic body was obtained.

EXAMPLES 16-19 Example 1 was repeated except that the plasticizer,mineral oil. was replaced by the following plasticizers: glycerin(Example 16), diethylene glycol (Example 17), dipropylene glycol(Example 18), and polyacrylic acid (Example 19). In each case theplasticizer was extracted with water and the end product was a strongporous ceramic material.

EXAMPLE 2O Thie example is intended to show the importance of theplasticizer in the filled polyolefin. A filled plastic material wasprepared from 66.7% by volume (90% by weight) a-alumina and 33.3% byvolume 10% by weight) particle form linear polyethylene of O melt index.The procedure of Example 1 (except, of course, for the plasticizerextraction step) was repeated. The resulting ceramic structure wasdistorted. one end was bubbly. and there was a hole through the centerof the structure.

EXAMPLE 21 EXAMPLE 22 The same composition as that used in Example I wasused, except that it was made into a sheet without-ribs. When fusiontook place the entire material fused giving a cylindrical structurecontaining micropores. but not any macropores. The porous ceramicstructure was very strong and hard enough to scratch glass.

EXAMPLE 23 Three Ceramic Bodies A",three Ceramic Bodies B. three CeramicBodies C". three Ceramic Bodies D were each impregnated with thefollowing catalytic components: 4.64% Cr O 6.96% MnO 4.64% CuO. and0.02% Pd. (percentages are by weight). The method of impregnation wasthat described heretofor.

A screen system" was used to determine the effectiveness of thecatalytic compositions on the porous base material prepared by theprocess of this invention. A feed composition consisting of thefollowing components was passed through the product of this invention: Nhexane and 750 ppm. carbon, 1000 ppm. NO. 1.0% CO. 2.0% 0 and 10.0% H O.

The inlet temperature (the point at which the feed composition enteredthe productof this invention) was about 300F. The temperature wasincreased 50 at about 15 minute intervals over a total period of 3hours. The results are given in the following Table I:

"/r of CO and HC removed from the feed composition steam.

For purposes of determining the effectiveness of the product of thisinvention it was decided to measure the amount of catalytic activity,hereafter referred to as activity. Activity graphs were prepared whereinthe horizontal axis represented temperatures ranging from 350 to 850F.and the vertical axis represented the amount of conversion of the basecomponent of the feed composition. With reference to the whole area ofthe rectangle fonned with base 350-850F." and altitude 0l00%conversion". the ratio of the area on the graph beneath the plotted lineto the whole area. times l00, was referred to as the percentage ofactivity. An ideal catalyst would, of course. have a percentage ofactivity of 100. For the particular catalytic component used in thisexample the percentage of activity" was obtained as follows:

It was also found that the temperature for a conversion of CO was 316F.and for HC the temperature was 506F. The temperature necessary for 50%conversion was 530F. for CO and 765F. for HC.

These results are comparable to those obtained when other forms ofcatalyst are used for auto exhaust control.

I claim:

1. A process for preparing an engine exhaust catalyst comprisingthefollowing steps:

a. homogeneously blending a composition consisting essentially of -80volume percent of a polyolefin having a molecular weight of at least150,000 and a standard load melt index of substantially zero. 5-67volume percent of a ceramic filler. selected from the group consistingof alumina. mullite, zir- Con mullite. magnesium aluminate spinel. andcordierite. and 1580 volume percent of a plasticizer selected from thegroup consisting of mineral oils. diethyleneglycol. proplylene glycol.dipropylene glycol glycerin. and a glycerol monoacetate, tri methyleneglycol. tetramethylene glycol. 2, 3-butylene glycol. triethyl phosphate.polyvinyl alcohol. and polyvinyl pyrrolidone,

b. heating said composition to about to 175C, molding to form a plasticsheet and impressing ribs thereon.

c. rolling said plastic sheet so that said ribs contact said sheet.heating to C. to just below the burn off point to fuse the contactingareas together thermoplastically.

d. extracting said plasticizer with water or an organic solvent.

e. removing said polyolefin by heating to 240 to 700C. to form a porousceramic structure, and to burn off the polyolefin and.

f. firing said porous ceramic structure at a temperature of 1300 to1450F. for about 2 hours to sinter said porous ceramic structure.

g. coating the ceramic structure with solutions of salts of metalsselected from the group consisting of the noble metals and copper,chromium and manganese and heating to reduce the noble metal salts tothe metal or convert the copper chromium and manganese salts to theoxides.

2. The process according to claim 1, wherein said polyolefin is selectedfrom the group consisting of polyethylene, and polypropylene. theplasticizer is mineral oil and the plasticizer is removed by contactingthe fused structure with hexane.

3. The process according to claim 1 wherein the solutions contain asufficient quantity of metal salts to prepare a catalyst containingabout 4 to 10 percent Cu). about 4 percent Cr- O 0 to 12 percent MnO and0.02 percent Pd.

1. A PROCESS FOR PREPARING AN ENGINE EXHAUST CATALYST COMPRISING THEFOLLOWING STEPS: A. HOMOGENEOUSLY BLENDING A COMPOSITION CONSISTINGESSENTIALLY OF 15-80 VOLUME PERCENT OF A POLYOLEFIN HAVING A MOLECULARWEIGHT OF AT LEAST 150,000 AND A STANDARD LOAD MELT INDEX OFSUBSTANTIALLY ZERO, 5-67 VOLUME PERCENT OF A CERAMIC FILLER, SELECTEDFROM THE GROUP CONSISGING OF ALUMINA, MULLITE, ZERCON MULLITE, MAGNESIUMALUMINATE SPINEL, AND CORDIERITE, AND 15-80 VOLUME PERCENT OF APLASTICIZER SELECTED FROM THE GROUP CONSISTING OF MINERAL OILS,DIETHYLENE GLYCOL, PROPYLENE GLYCOL, DIPROPYLENE GLYCOL GLYCERINE, AND AGLYCEROL MONOACETATE, TRIMETHYLENE GLYCOL, TETRAMETHYLENE GLYCOL, 2,3-BUTYLENE GLYCOL, TRIETHYLENE PHOSPHATE, POLYVINYL ALCOHOL, ANDPOLYVINYL PYRROLIDONE, B. HEATING SAID COMPOSITION TO ABOUT 125* TO175*C., MOLDING TO FORM A PLASTIC SHEET AND IMPRESSING RIBS THEREON, C.ROLLING SAID PLASTIC SHEET SO THAT SAID RIBS CONTACT SAID SHEET, HEATINGTO 150*C. TO JUST BELOW THE BURN OFF POINT TO FUSE THE CONTACTING AREASTOGETHER THERMOPLASTICALLY, D. EXTRACTING SAID PLASTICIZER WITH WATER ORAN ORGANIC SOLVENT,
 2. The process according to claim 1, wherein saidpolyolefin is selected from the group consisting of polyethylene, andpolypropylene, the plasticizer is mineral oil and the plasticizer isremoved by contacting the fused structure with hexane.
 3. The processaccording to claim 1 wherein the solutions contain a sufficient quantityof metal salts to prepare a catalyst containing about 4 to 10 percentCu), about 4 percent Cr2O3, 0 to 12 percent MnO2, and 0.02 percent Pd.3. REMOVING SAID POLYOLEFIN BY HEATING TO 240* TO 700*C. TO FORM APOROUS CERAMIC STRUCTURE, AND TO BURN OFF THE POLYOLEFIN AND, F. FIRINGSAID POROUS CERAMIC STRUCTURE AT A TEMPERATURE OF 1300* TO 1450*F. FORABOUT 2 HOURS TO SINTER SAID POROUS CERAMIC STTUCTURE, G. COATING THECERAMIC STRUCTURE WITH SOLUTIONS OF SALTS OF METALS SELECTED FROM THEGROUP CONSISTING OF THE NOBLE METALS AND COPPER, CHROMIUM AND MANGANESEAND HEATING TO REDUCE THE NOBLE METAL SALTS TO THE METAL OR CONVERT THECOPPER CHROMIUM AND MANGANESE SALTS TO THE OXIDES